1. Field of the Invention
The present invention relates to a direct acting pressure reducing valve.
2. Description of the Related Art
A direct acting pressure reducing valve is known in the art. The valve includes a main valve which is disposed in a communicating conduit via which a valve-inlet pressure introduction port and a valve-outlet pressure output port are communicatively connected with each other. The valve-outlet pressure output port is communicatively connected with a pilot pressure chamber which is formed by a diaphragm (flexible diaphragm member). The pilot pressure chamber and the valve-inlet pressure introduction port are communicatively connected with each other via a circular communicating hole, in which a connecting rod is inserted to be freely movable in a sliding manner. The connecting rod is disposed between the diaphragm and the main valve, and the pressure in the pilot pressure chamber acts on the diaphragm to be equilibrium with the spring force of a pressure regulating spring and controls the valve-outlet pressure by movement of the connecting rod in response to movement of the diaphragm. The connecting rod acts on the main valve to move the main valve in a valve closing direction thereof when the pressure in the pilot pressure chamber exceeds the spring force of the pressure regulating spring, while the connecting rod moves down in a direction to open the main valve so that the pressure which is determined with the pressure regulating spring is output from the valve-outlet pressure output port.
In this conventional direct acting pressure reducing valve, it is desirable that the direct acting pressure reducing valve operates sensitively to vary a cross-sectional area of the main valve so that the pressure in the pilot pressure chamber and the spring force of the pressure regulating spring are balanced. It is known experientially that the size of the circular communicating hole, via which the pilot pressure chamber and the valve-inlet pressure introduction port are communicatively connected with each other, has a very large influence on the responsivity to variations of the flow rate on the valve-outlet side. The circular communicating hole, via which the pilot pressure chamber and the valve-inlet pressure introduction port are communicatively connected with each other, and the connecting rod, which is inserted in the circular communicating hole to be freely slidably movable therein, are constructed so that the connecting rod can slidably move in the circular communicating hole normally with a minimum clearance therebetween. In this type of pressure reducing valve, the pressure responsivity of the valve-outlet pressure tends to be delayed in response to a sudden variation of the valve-inlet pressure. It is known that the valve-outlet pressure overshoots especially when a pressure supply valve on the valve-inlet side is opened.